The present invention relates to absorbent articles which are primarily designed to receive and retain bodily discharges such as urine. Such articles are disposable hygiene articles like baby diapers, training pants, adult incontinence articles and the like.
Absorbent Articles for receiving and retaining bodily discharges such as urine or feces such as disposable diapers, training pants, adult incontinence articles are well known in the art, and significant effort has been spent against improving their performance. The ability to provide better performing absorbent articles such as diapers has been contingent on the ability to develop relatively thin absorbent cores or structures that can acquire and store large quantities of discharged body fluids, in particular urine, and in particular with minimized tendency for releasing received liquid back to wearer""s skin.
In this regard, the use of certain absorbent polymers often referred to as xe2x80x9chydrogels,xe2x80x9d xe2x80x9csuperabsorbentsxe2x80x9d or xe2x80x9chydrocolloidxe2x80x9d or xe2x80x9chydrogel formingxe2x80x9d material has been particularly important. See, for example, U.S. Pat. No. 3,699,103 (Harper et al), issued Jun. 13, 1972, and U.S. Pat. No. 3,770,731 (Harmon), issued Jun. 20, 1972, that disclose the use of such absorbent polymers (hereafter xe2x80x9chydrogel-forming absorbent polymersxe2x80x9d) in absorbent articles. Indeed, the development of thinner diapers has been the direct consequence of thinner absorbent cores that take advantage of the ability of these hydrogel-forming absorbent polymers to absorb large quantities of discharged body fluids, typically when used in combination with a fibrous matrix. See, for example, U.S. Pat. No. 4,673,402 (Weisman et al), issued Jun. 16, 1987 and U.S. Pat. No. 4,935,022 (Lash et al), issued Jun. 19, 1990, that disclose dual-layer core structures comprising a fibrous matrix and hydrogel-forming absorbent polymers useful in fashioning thin, compact, nonbulky diapers. See also, U.S. Pat. No. 5,562,646 (Goldman et al.), issued Oct. 8, 1996 and U.S. Pat. No. 5,599,335 (Goldman et al.), issued Feb. 4, 1997, both of which relate to absorbent cores comprising regions of high concentrations of hydrogel-forming polymer, where the polymer forms a gel-continuous fluid transportation zone upon swelling.
In addition or alternatively to the use of hydrogel-forming absorbent polymers as the primary component in absorbent article storage structures, the use of polymeric foam materials derived from high internal phase water-in-oil emulsions (xe2x80x9cHIPEsxe2x80x9d) has been identified. See, e.g., U.S. Pat. No. 5,260,345 (DesMarais et al.), issued Nov. 9, 1993, U.S. Pat. No. 5,387,207 (Dyer et al.) issued Feb. 7, 1995, and U.S. Pat. No. 5,560,222 (DesMarais et al.), issued Jul. 22, 1997.
Further disclosure is made of structures having a low capacity in the regions between the legs of the wearer such as in PCT application U.S. 97/05046, filed on Mar. 27, 1997, relating to the movement of fluid through certain regions of the article comprising materials having good acquisition and distribution properties to other regions comprising materials having specific liquid storage capabilities. In the PCT publication WO 98/43570, absorbent structures are described providing improved fit in combination with improved rewetting performance.
Further prior art aimed at providing material with improved fluid acquisition/distribution performance, such as by providing xe2x80x9csurge management meansxe2x80x9d between the absorbent core and the topsheet, see for example EP-A-0.397.110 or EP-A-0.312.118.
Other documents disclose Absorbent articles with distribution layers underlying a storage layer which has a xe2x80x9cfluid passage wayxe2x80x9d allowing fluid to pass from the surface to the underlying distribution layer without penetrating the absorbent materials in a microscopic view (see for example EP-A-0.565.606 or EP-A-0.343.940). Alternative designs were described, where the fluid was enabled to penetrate through the overlaying storage layer because this layer has a relatively low ultimate storage capacity, such as by having only small amounts of superabsorbent material, see for example EP-A-0.512.010.
In U.S. Pat. No. 5,454,800 (Hirt et al.), absorbent articles are disclosed, comprising at least a first and a second absorbent member in a layered arrangement, such that lower layerxe2x80x94for example a paper tissuexe2x80x94has better wicking properties than the first layer, which can be made from large pore materials such as co-form or air-laid tissue webs, or which can have gaps or apertures to allow fluid penetration into the under-laying layer.
Yet other articles describe the use of superabsorbent materials for being used in absorbent structures, whereby the materials exhibit a liquid permeability, expressed in xe2x80x9cSaline Flow Conductivityxe2x80x9d, end as described in U.S. Pat. No. 5,599,335.
A further class of documents describe materials having improved fluid distribution properties, such as having high flux as disclosed in EP-A-0.809.991 or high wicking capability as disclosed in copending U.S. patent application Ser. No. 09/042418, filed Mar. 13, 1998 by T. DesMarais et al. titled xe2x80x9cAbsorbent materials for distributing aqueous liquidsxe2x80x9d.
However, a problem with using distribution materials as described in such art is that a relatively high capillary absorbent pressure is required for the storage materials to drain the distribution materials, and to maintain good rewet performance of the article.
Thus, there is still a need to improve towards well performing articles, which provide good acquisition, good distribution without detrimentally affecting comfort of the wearer, such as providing low thickness, prevent a hard feel especially on the outer side of the article (often referred to as xe2x80x9cpoly-pockmarkingxe2x80x9d), which even might cause liquid to penetrate through. In particular, the combination of low thickness with small core sizes resulted in the need for overall xe2x80x9cbasis capacitiesxe2x80x9d, i.e. high amounts of fluid storage capacity per unit area.
Henceforth, it is an object of the present invention to provide an absorbent article with improvements in the above mentioned areas, in particular to provide an absorbent article which is easy to manufacture, even on conventional production lines.
It is a further object of the present invention to provide an absorbent article, which exploits the benefits of particularly suitable distribution materials with fluid storage materials or members of conventional type.
The present invention is an absorbent article, such as for use in hygienic applications, which has an ultimate fluid storage region, and a fluid distribution region positioned between the ultimate storage region and the garment oriented surface of the article, which is in fluid communication with the ultimate fluid storage region, whereby the ultimate fluid storage region comprises material which has (1) a Capillary Sorption Desorption Capacity at 100 cm (CSDC 100) of at least 10 g/g; which further has (2) a Capillary Sorption Desorption Capacity at 0 cm (CSDC 0) higher than said CSDC 100 and which thereby has (3) a Loosely Bound Liquid Capacity (LBLC) as the difference between (CSDC 0 and CSDC 100); and which has (4) a Capillary Sorption Desorption Release Height when 50% of said LBLC are released (CSDRH 50) of less than 60 cm. Further, the liquid distribution layer comprises material having a Capillary Sorption Absorption Height at 30% of its maximum capacity (CSAH 30) of at least 25 cm.
Additionally, the ultimate fluid storage region can have a SFC value of more than 25xc3x9710xe2x88x927 cm3sec/g., preferably more than 70xc3x9710xe2x88x927 cm3sec/g, more preferably more than 100xc3x9710xe2x88x927 cm3sec/g, even more preferably more than 200xc3x9710xe2x88x927 cm3sec/g, most preferably more than 400xc3x9710xe2x88x927 cm3sec/g or even more than 1000xc3x9710xe2x88x927 cm3sec/g.
In a further aspect, the present invention can have a fluid distribution region material having a CSAH 30 of at least 50 cm.
In yet another aspect, the fluid distribution region material has a CSDH 50 of less than 150 cm. Alternatively, the benefits of the fluid distribution material can be described by having a fluid permeability value at 50% saturation (k(50)), which is at least 15% of the permeability value at 100% saturation (k(100)), preferably more than 18%, even more preferably more than 25% and most preferably more than 35% of the permeability value at 100% saturation (k(100)).
In yet another aspect, the fluid distribution region material has a permeability at 100% saturation (k(100)) of at least 1 Darcy, preferably of at least 8 Darcy.
In a preferred embodiment of the present invention, the distribution region material has a expansion factor of at least 4, preferably of at least 5, more preferably of at least 8, and most preferably of at least 15.
Another preferred execution of the present invention has distribution region material having a Cumulative Flux value at 15 cm in the Vertical Wicking test of at least 0.02 g/cm2/min, preferably more than 0.04, even more preferably of more than 0.07 g/cm2/min, and most preferably more than 0.14 g/cm2/min.
Suitable materials for being useful for the present invention as fluid distribution and/or storage component can be foam materials, preferably polymeric foam material, and even more preferably polymeric foam material which is derived from high internal phase water-in-oil emulsions.
Alternatively, the distribution region can comprise fibrous material, preferably chemically stiffened cellulose, and/or synthetic fibers. Optionally, the distribution material can be mechanically treated after formation.
The distribution region according to the present invention can be a single layer material or is comprised of several layers, can be of essentially homogeneous composition and/or density and/or basis weight.
The ultimate fluid storage region can comprise fibrous material, preferably, this region comprises superabsorbent materials. Preferably, these materials have a SFC of at least 50xc3x9710xe2x88x927 cm3sec/g, preferably of at least 80xc3x9710xe2x88x927 cm3sec/g more preferably of at least 100 cm3sec/g, and even more preferably of at least 150 cm3sec/g.
The ultimate fluid storage region can be essentially homogeneous in composition, and can be a single or multi-layered structure. Preferably, the storage region is essentially free of void, apertures, or gaps having an individual void, aperture or gap volume of more than 10 mm3.
When the absorbent article of the present invention is sectioned into a crotch and one or more waist regions, the crotch region can have a lower ultimate fluid storage capability than one or more waist region together, preferably less than 49%, more preferably less than 41% and even more preferably less than 23% of the total core ultimate fluid storage capacity.
In yet another aspect, the present invention is an absorbent article which has a relatively low basis weight of the liquid storage member of less than 450 g/m2, and for which the basis weight of the liquid storage member is essentially constant throughout it, such as by having the basis weight of the ultimate storage material in the crotch region differing by less than 20% (dry weight basis) throughout the article.
In yet another aspect the absorbent article according to the present invention has a length of the crotch region which is half of the length of the total absorbent core. In a preferred embodiment the ultimate fluid storage region covers a surface area of at least 1.2 times the surface area of said fluid distribution region.